The present invention relates to new fluorine-containing organosilanes and to their use to improve the lubricity and wear characteristics of magnetic recording media. More specifically, this invention relates to organosilanes having fluoroalkyl groups and acyloxypolyalkyleneoxy or alkoxypolyalkyleneoxy groups.
Magnetic recording media such as audio recording tapes, video recording tapes, and computer information recording disks must contact and often move across other machine parts during use. For instance, video tape moves across the magnetic head and through tape guides at high velocities in modern video tape recorders. Tapes suitable for these recorders must have good wear resistance and relatively low coefficients of friction if they are going to run smoothly and steadily for extended periods. If a tape has too high a coefficient of friction, it may vibrate when it passes through tape guides or over magnetic heads, so that recorded or reproduced signals are distorted from the originals. In some cases, a so-called "Q" sound due to vibration of the magnetic tape is encountered.
In order to reduce vibration and wear, efforts have been made to impart lubricity and smoothness to magnetic recording media. For example, polydimethylsiloxanes, castor oil, molybdenum disulfide, graphite, and higher fatty acids have been suggested as lubricants for magnetic recording tape. Such lubricants are often included in magnetic paint compositions so that the lubricant is mixed throughout the magnetic layer when the paint is applied to the recording media substrate. The extent of improved wear that can be obtained is however limited with these materials because when increased quantities are used in the magnetic layer, a phenomenon called "blooming" occurs. Blooming is caused by lubricating agent exuding out of the magnetic layer. When blooming occurs, the surface of the magnetic tape gets rough and the magnetic properties of the medium deteriorate rapidly. Consequently, there is a need for improved lubrication agents that will provide good lubricity and at the same time exhibit improved compatibility so that blooming does not occur.
U.S. Pat. No. 4,007,313 discloses the use in magnetic layers of organosilanes having the formula: EQU CF.sub.3 CH.sub.2 CH.sub.2 (CH.sub.3).sub.3-n Si(OOCR).sub.n
where R is a saturated or unsaturated aliphatic group, having from 7 to 17 carbon atoms, and n is an integer in the range of 1 to 3. It is taught that magnetic recording tape containing these silanes has a reduced coefficient of friction and improved wear resistance. Similarly, Japanese Patent O.P.I. No. 92,428 (1982) discloses magnetic recording media having a magnetic layer containing an organosilane of the formula: EQU F(CF.sub.2).sub.m (CH.sub.2).sub.p Si(CH.sub.3).sub.n (Z).sub.3-n
where Z is R.sub.f COO--, R.sub.f SO.sub.3 --, or R.sub.f COO(CH.sub.2 CH.sub.2 O).sub.k -- with R.sub.f being defined as a saturated perfluoro hydrocarbon group having 1 to 20 carbon atoms, m is 1 to 20, n is 0 to 2, p is 2 to 20, and k is 1 to 50. The organosilane is said to improve abrasion resistance of magnetic media.
U.S. Pat. No. 4,308,212 discloses another class of organosilanes having the general formula: EQU F(CF.sub.2 CF.sub.2).sub.n CH.sub.2 CH.sub.2 Si(OOCR').sub.m (R).sub.3-m
where R is a monovalent hydrocarbon group having from 1 to 6 carbon atoms, R' is a monovalent hydrocarbon group having from 7 to 21 carbon atoms, n is a positive integer not exceeding 4 and m is a positive integer not exceeding 3. It is taught that these organosilanes can be applied to the surface of synthetic resins to improve their surface lubricity. Also, coating compositions containing synthetic resins are said to be improved by addition of these organosilanes.
Finally, U.S. Pat. No. 4,469,751 discloses still another class of organosilanes having the general formula: ##STR2## where R represents a saturated or unsaturated monovalent hydrocarbon group having from 7 to 21 carbon atoms, R' represents a saturated monovalent hydrocarbon group having from 1 to 4 carbon atoms, k is an integer of from 1 to 12, p is an integer of from 2 to 6, m is an integer of 1 or 2, and m is an integer of 1 or 2 provided that m+n is 3 or less. These organosilanes are described as lubricants for magnetic layers in recording media.